Valve drive of an internal combustion engine

ABSTRACT

A valve drive ( 1 ) including of a hydraulic support element ( 2 ), a finger lever ( 18 ) supported on the support element ( 2 ), and a cam ( 25 ) of a camshaft ( 26 ), is provided with opening mechanisms ( 27, 28, 29 ) for the forcible opening of a check valve ( 14 ) of the support element ( 2 ) during contact of a base circle (α) of the cam on the finger lever ( 18 ). The opening mechanisms ( 27, 28, 29 ) are formed from a slide extending in a support element, which acts on a closing body ( 13 ) of the check valve ( 14 ). In addition, they include a separate lever for the slide, where this lever communicates with a signal path on the camshaft ( 26 ). By these measures, eccentricity of the base circle (α) or the like no longer lead during a play compensation phase of the support element ( 2 ) to an undesired hardening of a high pressure chamber ( 12 ) of the support element ( 2 ).

BACKGROUND

The invention relative to a valve drive of an internal combustion enginewith the following characteristics:

a) the valve drive includes of a hydraulic support element, a fingerlever and a cam of a camshaft or a plurality of these structural parts;

b) the support element is installed with its housing into a cam-sidebore of a cylinder head, whereby a pressure piston that is axiallymovable relative to the housing and located in a bore of the housingprojects with its head beyond the cylinder head in the direction of thecam, whereby between a bore-side bottom of the housing and a bore-sideweb of the pressure piston, a high pressure chamber for a hydraulicmedium is located, which high-pressure chamber can be closed by aclosing body of a check valve attached to the web in the directiontoward a supply chamber or a supply line enclosed by the pressurepiston;

c) the finger lever is constructed like a beam and has lateral surfacesnear the cam and away from the cam, whereby it acts via a first end ofthe lateral surface away from the cam on at least one gas exchange valvein the direction of the stroke and is supported via a second end of thelateral surface away from the cam on the head of the pressure piston sothat it can move by pivoting;

d) the cam acts on a contact section that lies between the ends of thecam-side lateral surface of the finger lever.

A valve drive of this type is known from the prior art from the document“Hydraulic Valve Lash Adjustment” (page 9) from August 1996, publishedby the applicant. It is disadvantageous in this that eccentricity of thecam base circle, transverse oscillations of the camshaft, brought on forexample by auxiliary cams for injection pumps, or camshaft bearing playin the base circle can cause the high pressure chamber of the hydraulicsupport element to become hardened and the gas exchange valve opens in amost unfavorable way. Even in so-called transient operation of theengine, in particular during extremely cold environmental temperatures,the fall rate of the hydraulic support element is not sufficient tocompensate for the positive dilatations on the gas exchange valveinvolved, preferably the outlet valve. In addition, in hydraulic supportelements that have been constructed until now, a closing structure ofits check valve must be opened with motor oil pressure. Thus, a certaintime delay until the completion of the play compensation must be takeninto account. This delay is a function of the instantaneous differentialpressure incident on the check valve.

The object of the invention is thus to create a valve drive of theabove-mentioned type, in which the cited disadvantages are eliminated.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved in that the valvedrive is provided with opening mechanisms for the positive or compulsoryopening of the check valve of the support element during contact of abase circle of the cam on the lever.

By these measures and in particular in combination with the mechanismsdisclosed, the disadvantages cited at the beginning are effectivelyeliminated.

By the fact that positive opening is done in the base circle of theclosing body of the check valve via the slide, the high pressure chamberis no longer hardened when the operating conditions described aboveoccur. During the defined base circle window, an unhindered overflow byhydraulic agent from the high pressure chamber into the supply chamber(or the supply line), and vice-versa, is enabled. It is also successfulto design the spring element for the closing body of the check valve sothat it is clearly stronger in its force than spring elements designedpreviously for support elements until now. This improves the dynamicbehavior of the support element.

The opening mechanisms are preferably formed out of the aforementionedslide for the closing body, which can be impinged by a separate lever.This lever in turn communicates with at least one signal path providedon the cam. In particular, the signal path is positioned as a componentof the opening mechanism on the cam axially adjacent to it and isdesigned with an approximately circular shape. In this manner,preferably on both sides, edge areas of the base circle of the cam andpreferably, but not necessarily, the remaining path section outside ofthe base circle (cam catch flank, cam peak, cam drop flank) can be setat a lower radius than the base circle window. Thus, the slide is movedover the signal path that is raised in the base circle, which acts onthe separate lever, moving it in such a way in the bore direction of thesupport element that the closing structure is opened forcibly andprevented from closing.

Edge areas of the base circle, which border on the cam catch flank andcam drop flank, are therefore designed lowered in radius so that thefill valve lift is available when the closing body for the gas exchangevalve is closed. Otherwise, the loss in lift must be compensated by anincreased cam contour.

In a preferred embodiment, a two-piece slide is proposed, whichpreferably has a rod-like construction. Also conceivable, however, areother geometries and/or also non-axially running slides, but ratherthese types of mechanisms acting radially or slanted on the closingbody. Likewise, triggered external impingement mechanisms such aselectromagnets and the like can be used to dislocate the closing bodyduring the base circle phase.

According to an advantageous embodiment of the invention, the separatelever should be attached on the second end of the finger lever. A simpleattachment form is created in that the lever has in the section of theend, a bent projection which has a clip. Using this clip, it can beattached in a simple way to the second end of the finger lever. As analternative to this, it is also contemplated to insert a joint as abearing for the second lever and/or to arrange the second leverseparately relative to the cylinder head or an additional structuralpart arranged in the cylinder head.

A measure favorable in terms of wear is provided in an additionalsubordinate claim. According to the measure, the separate lever shouldbe expanded in its contact area to the signal path or to the slide orprovided with suitable wear protection measures such as a heattreatment. In this way, the life of the lever is clearly improved or itswear is reduced. If possible, this separate lever, as well as the fingerlever as such, can be dimensioned so that it is thin-walled or made froma light construction material.

A first part of the proposed two-piece slide runs advantageously in thesecond end of the finger lever, whereby the finger lever has as a restfor the head of the pressure piston of the support element, adome-shaped recess. The first part is spring-loaded in the cam directionvia a spring element, such as a compression spring. Thus, in theunloaded state of the signal path, the first part is removed via thespring element from the area of the dome-shaped recess. In this way, thefirst part can no longer come into contact with the head of the pressurepiston when the finger lever is pivoted. At the same time, the secondpart of the slide, which is adjacent to the first part, is made so thatits length is such that it also does not project into the area of thedome-shaped recess when it is unloaded, so that it has a contact to thebase of this recess.

In a further embodiment of the invention, it is proposed to guide thesecond part of the slide over a head of the pressure piston, which isconstructed so that it is solid, for example, where the pressure pistonthen has a longitudinal bore. It can be provided, however, also, toarrange inside the pressure piston, preferably in this supply chamber, aseparate washer or a similarly suitable mechanism, over which the secondpart is additionally conducted. Should the pressure piston not beconstructed so that it is solid, but instead, for example, from a sheetmetal material, then in the head area, separate sheaths or similarlyused elements can be applied. Also, it is conceivable to guide the firstpart via support plates or the like which emerge from the sides of thefinger lever and extend in the cam direction and then are bent in thedirection of the second part.

It is proposed to construct the check valve as a ball valve. This valvecan be manufactured in a cost-effective way or obtained as a massproduction part. As mentioned, the spring element, which impinges theclosing body of the check valve in the closing direction, can bedesigned so that it has a relatively strong spring force. In this way,an immediate closing of the overflow bore is to be taken into account atthe desired point in time; i.e. prior to the beginning of the cam catchflank. It is also conceivable, however, to have a plate valve or asimilar solution.

An additional measure for reducing the friction is proposed in that thecontact section of the finger lever is manufactured as a roller, whichcan be constructed selectively so that it is set in roller bearingsopposite the finger lever.

It is also conceivable to position the separate lever on both sides ofthe finger lever in a fork-like manner, such that transverse moments canno longer act on it. It is advantageous to arrange the signal path alsoon both sides of the cam. Also, it is provided to reverse theimpingement form of the slide. According to this, the slide can beimpinged via a spring force in the unloading direction of the checkvalve, and pulled back via the control contour that acts on the separatelever.

In addition it is proposed to couple at least one of the parts of theslide along the length in the valve drive. In this way, a tolerance of alift of the closing structure can be adjusted to be relatively small.

The measures according to the invention also provide the advantage thatan excellent ventilation of the high pressure chamber is achieved. Inthis way, additional ventilation measures can be omitted and the entireconstruction height of the support element can be clearly minimized.Possibly, a supply room is no longer necessary for the hydraulic medium.In this way, in turn, the length of the slide can be minimized. The highpressure chamber itself defines only a small volume and the additionalaxial stoppers for the pressure piston, until now made on the housing,can be omitted.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in greater detail functionally using thedrawing.

The only drawing shows a cross-section through the valve drive accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawing shows a valve drive 1, whose basic construction is known tothe skilled artisan from the design. This valve drive 1 includes of ahydraulic support element 2, which is installed with its housing 3 in abore 4 of a cylinder head 5. In a bore 6 of the housing 3, a pressurepiston 7 is integrated that is axially movable relative to the housing.This pressure piston 7 includes a head 8 that projects beyond the bore4.

A bottom 9 of the housing 3 extends at least indirectly opposite a base10 of the bore 4. At the same time, the pressure piston 7 has on thebore side a radially inwardly extending web 11. Between the web 11 andthe bottom 9, a high pressure chamber 12 is made for a hydraulic medium.At the same time, on the web 11, a closing body 13 of a check valve 14is attached. This closing body 13 is constructed as a ball and isimpinged in the closing direction by a spring element 15, heremanufactured as a compression spring. The closing body 13 closes anoverflow bore 16 positioned in the web 11. At the same time, thepressure piston 7 is impinged in a direction away from the bore 4 by anadditional spring element 17.

On the head 8 of the pressure piston 7, a finger lever 18 is supportedin the area of its second end 19. For this purpose, the finger lever hason its lateral surface 20 that is away from the cam, a dome-shapedrecess 21. The head 8 in turn has at least in its contact area to therecess 21, a complementary form.

In the area of its first end that is located on the lateral surface 20away from the cam, the finger lever 18 acts on at least one gas exchangevalve (not shown) in the stroke direction.

A cam-side lateral surface 23 of the finger lever 18 has, between thefirst and the second ends 22, 19, a contact section 24 for a cam 25 of acamshaft 26. This contact section 24 is constructed as a roller, whichwill not be explained further here, which runs on an axle 46 arrangedperpendicularly in the finger lever 18.

According to the invention, the valve drive 1 is provided with openingmechanisms 27, 28, 29. These cause a forcible opening of the check valve14 during contact of a base circle α of the cam 25 on the finger lever18. The opening means 27 is manufactured as a slide with a rod-typeconstruction and runs preferably axially in the pressure piston 7.Preferably, the opening means 27includes a first part 30 and a secondpart 31. The first part 30 is arranged in a receptacle 32 that extendsthrough the recess 21 and is impinged by an spring element 33, such as acompression spring, in the cam direction. The first part 30 borders thesecond part 31. This second part 31 is guided directly in the pressurepiston 7 and acts with its other end 34 in the opening directiondirectly on the closing body 13.

A first end 35 of the first part 30 is impinged by an additionalcomponent of the opening mechanism. This is constructed here as aseparate lever 28. The lever 28 has on one end a contact area 36, bywhich it communicates with a third component of the opening mechanism.This third component is formed as a signal path 29 for the separatelever 28. The signal path 29 extends preferably axially adjacent to thecam 25 on the camshaft 26 and has in principle a circular geometry.However, it has an area with a reduced radius on the edge areas 37, 38on both sides of the base circle α as seen in the rotation direction,and over the remaining circumferential section β. The circumferentialsection β extends over the cam height; i.e. the cam catch flank, the campeak and the cam drop flank.

At the same time, it can be ascertained from the drawing that theseparate lever 28 has approximately in the area of its center on a side39 facing away from the cam, a contact area 40 for the first end 35 ofthe first part 30 of the slide 27. In the area of the second end 19, theseparate lever 28 makes a transition into a bent catch 42. This catchhas a clip 43, by which it is attached on the second end 19 of thefinger lever 18 so that it can pivot.

As can be ascertained from the drawing, the signal path 29 impinges theseparate lever 28 in the base circle α in such a way that the slide 27with its parts 30, 31 is translated axially in the direction to thesupport element 2. In this way, the closing body 13 is moved in thedirection into the high pressure chamber 12, such that the overflow bore16 is forcibly opened. Thus, during the aforementioned base circlephase, an unobstructed and forcible overflow of hydraulic agent out ofthe high pressure chamber 12 into a supply space 44 enclosed by thepressure piston 7 or in a supply line (not shown) and in reverse, ismade possible. Disadvantageous transverse oscillations of the camshaft26 or eccentricity in the base circle α of the cam 25 and the like, asin the prior known state of the art can no longer lead to the undesiredhardening of the high pressure chamber 12 and possibly cause unloadingor opening of the impinged gas exchange valve during the base circlephase. In the rotational direction of the cam 26, the edge area 38 ofthe signal path 29 extends from to the base circle α as a component ofthe base circle α. This edge area 38 and the other circumferentialsection β and the following edge area 37 (which in turn transitions tothe beginning base circle α) are reduced in their radius opposite theradius of the base circle α, in a quasi-groove shape. In this manner, adepth for the circumferential section β with edge areas 37, 38 isselected so that the separate lever 28 is unloaded via the force of thespring element 33, 15 as far in the direction of the cam so that theclosing body 13 can exert its closing function. If necessary, theseparate lever 28 can be supported in its movement in the cam directionby elastic means (not shown in greater detail).

Reference Number List

1 Valve drive

2 Support element

3 Housing

4 Bore

5 Cylinder head

6 Bore

7 Pressure piston

8 Head

9 Bottom

10 Base

11 Web

12 High pressure chamber

13 Closing body

14 Check valve

15 Spring element

16 Overflow bore

17 Spring element

18 Finger lever

19 Second end

20 Lateral surface away from cam

21 Dome-shaped recess

22 First end

23 Cam-side lateral surface

α Base circle

β Circumference section

24 Contact section

25 Cam

26 Camshaft

27 Opening mechanism, slide

28 Opening mechanism, separate lever

29 Opening mechanism, signal path

30 First part

31. Second part

32. Receptacle

33. Spring element

34. Other end

35. First end

36. Contact area

37. Edge area

38. Edge area

39. Facing side away from cam

40. Contact area

41. not given

42. Catch

43. Clip

44. Supply chamber

45. Guide bore

46. Axis

What is claimed is:
 1. Valve drive (1) of an internal combustion engineincluding the following: the valve drive (1) includes a hydraulicsupport element (2), a finger lever (18) and a cam (25) of a camshaft(26) or a plurality of these structural parts; the support element (2)includes a housing (3) that is installed into a cam-side bore (4) of acylinder head (5), so that a pressure piston (7) that is axially movablerelative to the housing (3) and located in a bore (6) of the housing (3)projects with its head (8) beyond the cylinder head (5) in the directionof the cam, whereby between a bore-side bottom (9) of the housing (3)and a bore-side web (11) of the pressure piston (7), a high pressurechamber (12) for hydraulic medium is formed, where the high-pressurechamber (12) being closeable by a closing body (13) of a check valve(14) attached to the web (11) in the direction toward a supply chamber(44) or a supply line enclosed by the pressure piston (7); the fingerlever (18) is constructed as a beam and includes lateral surfaces (23,20) near the cam and away from the cam, whereby it acts via a first end(22) of the lateral surface (20) away from the cam on at least one gasexchange valve in a direction of stroke and is supported via a secondend (19) of the lateral surface (20) away from the cam on the head (8)of the pressure piston (7) so that it can move by pivoting; the cam (25)acts on a contact section (24) that lies between the ends (22, 19) ofthe cam-side lateral surface (23) of the finger lever (18);characterized in that the valve drive (1) is provided with means forcompulsory opening of the check valve (14) of the support element (2)during contact of a base circle (α) of the cam (25) on the finger lever(18), comprising a slide (27), a separate lever (28) and a signal path(29) located on the cam (25), whereby the slide (27) is arranged in thesupport element (2) and includes a first end (35) that projects axiallybeyond the head (8) and with another end (34) impinges the closing body(13) of the check valve (14), the first end (35) contacts the separatelever (28), which contacts the signal path (29) on one end and on theother end, is pivotably attached to the second end (19) of the fingerlever (18) or the cylinder head (5).
 2. Valve drive according to claim1, characterized in that, the signal path (29) is arranged axiallyadjacent to the cam (25) on the camshaft (26) and includes outside thebase circle (α) of the cam (25), at least in edge areas (38, 37) on bothsides of the base circle (α) on its cam catch flank and cam drop flank,a circumferential section (β) that is reduced in radius.
 3. Valve driveaccording to claim 1, characterized in that, the separate lever (28)makes a transition in the area of the second end (19) of the fingerlever (18) into a catch (42) that extends approximately perpendicular toa longitudinal extension direction of the lever (28) and is connectedvia a clip (43) or a joint to the second end (19).
 4. Valve driveaccording to claim 1, characterized in that, the separate lever (28) isexpanded in a contact area (36, 40) to the signal path (29) or to theslide (27) or provided with suitable wear protection measures includinga heat treatment or an applied layer.
 5. Valve drive according to claim1, characterized in that, the finger lever (18) or the separate lever(28) is made out of a sheet metal material or a light constructionmaterial.
 6. Valve drive according to claim 1, characterized in that,the slide (27) is made in two pieces, wherein a first part (30) extendsinto the second end (19) of the finger lever (18) and is impinged by theseparate lever (28), and wherein a second part (31) is arranged in thepressure piston (7) and communicates with the closing body (13) of thecheck valve (14), with both parts (30, 31) being adjacent to each other.7. Valve drive according to claim 6, characterized in that, the secondend (19) of the finger lever (18) has a dome-shaped recess (21) in whichthe head (8) of the pressure piston (7) is seated, whereby the firstpart (30) of the slide (27) is spring-loaded via an spring element (33)in the cam direction, so that when it is uncompressed the separate lever(28) is outside of a contact area from the head (8) of the pressurepiston (7), and whereby the second part (31) of the slide (27) is made asufficient length so that it is out of contact with the recess (21) whenit is uncompressed by the separate lever (28).
 8. Valve drive accordingto claim 1, characterized in that, the check valve (14) is constructedas a ball valve, whereby the ball is impinged in the closing directionby a spring element (15).
 9. Valve drive according to claim 1,characterized in that, the head (8) of the pressure piston (7) is solidwith a guide bore (45) for the slide (27).
 10. Valve drive according toclaim 1, characterized in that, the contact section (24) of the fingerlever (18) is made as a roller, which runs on a roller bearing on anaxle (46) arranged in the finger lever (18).
 11. Valve drive accordingto claim 6, characterized in that, at least one of the parts (30, 31) ofthe slide (27) is coupled lengthwise in the valve drive (1).